You will receive emails from the mailing list and also from the bug tracker if developers need your help.
Also, there will be announcements of new releases and preview releases on the mailing list, which give you the possibility to test releases early and to help the developers fix them.

There are many different setups, and people have different interests.
If we want ownCloud to run well on NGINX, for instance, someone has to test this configuration.
Furthermore, during bug fixing the ownCloud developers often do not have the possibility to reproduce the bug in a given environment, nor are they able confirm if it was fixed.

As a member of the Test Pilot Team you could act as a contact person for a particular area to help developers fix the bugs you care about.
Testing ownCloud before it is released is the best way of making sure it does what you need.

Another benefit is a closer relationship with the developers, because you will know which people are responsible for which parts, and it will be easier to get help.

If you want, you can also be listed as an active contributor on the owncloud.org page.

Testing is a matter of trying out some scenarios you decide on or were asked to test, for example, sharing a folder and mounting it on another ownCloud instance.
If it works – awesome, move on.
If it doesn’t, find out as much as you can about why it doesn’t and use that for a bug report.

This is the stage where you should see if your issue is already reported by checking the relevant bug tracker.
It might even be fixed, sometimes!
Alternatively, just ask on the test-pilots mailing list.

Finally, if the issue you bump into is a definite bug and the developers are not aware of it, file it as a new issue in the relevant bug tracker.